Electrolytic grinding apparatus



Jan. 22, 1957 G. E. COMSTOCK 30 2,778,794

ELECTROLYTIC GRINDING APPARATUS Filed March 16, 1953 4 Sheets-Sheet 1 n F7 5, Z

INVENTOR. GEORGE E. CEI/VI5TUE'K,EIR'IU.

ATTORNEY Jan. 22, 1957 G. E. COMSTOCK 3D 2,778,794

ELECTROLYTIC GRINDING APPARATUS Filed March 16, 1953 4 Sheets-Sheet 2 Z2 6/\ GT 2/ Z Fl G'. 5

INSULA T/ON 35 t 29 CR 30 JNVENTOR. M/SULAT/ON GEURGE E. CUMSTUUK RJJ.

FIG. 4 7. X444 A TTOFf/VEY Jan. 22, 1957 s. E. coMsTocK 30 2,778,794

ELECTROLYTIC GRINDING APPARATUS Filed March 16, 1955 4 Sheets-She et :5

BY Ma 7%.; m

AT TURNEY United States Patent 2,7 3, 94 RQ H GRINDING AJPABAIUS Qeorge E. Cornstock 3d, Holden, Mass., assignor to Nqrton mran Wa asteu Ma s, a ummation of Massachusetts Application March 16, 1953, Serial No. 342,311

lscaims .(c 204-21 This invention relates to electrolytic grinding and more particularly to an electrolytic grinding system and apparatus. v v

One of the objects of this invention is to provide a snnple, compact and efiicient system'and apparatus for controllably elfecting electrolytic stock removal from the work-piece and thatis adapted for ready and convenient installation in factories or plants already provided with circuits or sources of alternating current electrical'energy. Another object is to provide an electrolytic grinding sys- .tem and apparatus of the just mentioned character in which conversion of alternating current electrical energy to unidirectional electrical energy at the locus'of electrolytic stock removal may be achieved in a dependable, efiicient and relatively low-cost manner and with simple and efiicient controls that act in response to conditions at thelocus of stock removal for achieving efiicierit, safe and substantially self-protecting electrolytic decomposition at the face of the work-piece. Another 'object is to provide a compact, simple and dependable electrolytic grinding and energy-supply system therefor in which T 611- version of alternating current electrical energy to unidirectional electrical energy at the locus of stock 'removal may be efliciently effected, in response to changing electrical conditions at the locus of stock removal so as to provide, for electrolytic decomposition actionfco'ntrollable voltage and current characteristics that are opti mum or most desirable for effecting electrolytic decomposition and for protecting against undesired or damagmg current concentrations or arcing.

Another object is in general to provide improved electrolytic grinding apparatus and control systems'ther'efor in which complications of arrangements and circuits and control equipments, or wastefulness of "electrical energy, of systems heretofore proposed may be dependably lessened or avoided.

Another object is to carry out the above-mentioned objects, severally or jointly, in which the apparatus and system, supplied initially from an alternating current source, effect, in a simple and dependable mariner, controls at the direct-current locus of electrolytic work-piece decomposition whether the conductive grinding wheel consists of a single rotating conductive element or comprises a plurality of coacting rotating conductive elements capable of both individual and conjoint coaction, with or without accompanying or concurrent abrasive action on the work-piece. v r i Another object is to provide a system and apparatus for electrolytic stock removal from a work-pieceatlrat will be compact, dependable, efiicient, and well adaptled for industrial uses and installation; Other objects will be in part obvious or in part pointed out hereinafter.

The invention accordingly consists inthe features .of construction, combinations of elements, arrangements ,of parts and in the several steps andrelation and order of each of the same to one or more of the others thereof, all aswill be illustratively described herein, and the scope "ice of the application of which will be' indicated in the following'claiins.

In the accompanying drawings, in which are shown illustratively themechanical and electrical features of my" invention and in which similar reference characters refer to several parts throughout the several views of the drawings,

Figure 1 is a front elevation, with certain parts shown 01' indicated diagrammatically, of the grinding machine;

Figure 2 is a fragmentary side elevation thereof;

Figure 3 is a fragmentary horizontal sectional view on an enlarged scale, showingcertainmechanic'al and electrical features of one form of grinding wheel in relation to a work-holder and certain electrical features related thereto;

Figure 4 is a fragmentary horizontal sectional view on an enlarged scale, showing certain mechanical and electrical features of another form of grinding wheel in relation to a work-holder and certain electrical features related thereto; i

Fi'gurS is a fragmentary or detached front elevation of a wheel guard cover' and associated electrolyte-dis tributing'parts as related to the grinding wheelof Figure 3 and as seen from the front in Figure 1' and from the left in Figure 3; i

Figure 6' is a fragmentary or detached front elevation of a wheel'cover and associated electrolyte-distributing parts as related't'o the grinding Wheel of Figure 4 and as "seen from the front in Figure l and from the left in .F i i v "Figure 7 is a diagrammatic representation of the apparatus utilizing a single rotating conductive element or ring, such as the g'rinding'wheel of Figures 3 and 5, and of the electrical energy supply system associated therewith and of the coacting controls therefor;

" Figure 8 is a diagrammatic representation of the appara'tus utilizing multiple rotating conductive elements or rings, such as the grinding wheel of Figures 3 and 6, and 'of the electrical energy supply system' associated therewith and of the coacting controls therefor;

Figure 9 is a diagrammatic representation like that of Figure 7 but showing a modification thereof, and

Figure 10 is a diagrammatic representation like that of Figure 8, but showing a modification thereof.

As conducive to a clearer understanding of certain features of my invention itmay here be noted that'there are many advantages to .be gained in stock removal by electrolytic grinding in which, by the coaction of an electrolyte and direct or unidirectional current, stock is removed from the work-piece by electrolytic decomposition of the work face, especially for machining hard cemented carbides (such as cobalt-bonded tungsten and/or titaniumcarbide) whereby, when the rotating conductive element or face of the grinding wheel contains abrasive grain, the cutting action of the abrasive grain may be very materially supplemented. Most industrial plants or factories are equipped'with or WlICClfOI' alternating current energy, usually and illustr'atively three-phase and of 60 cycles. One of the objects of my invention is to provide efiicient and dependable electrolytic grinding apparatus and compact, simple, andcoacting controllable energy supply system that needs only to be electrically connected to the existing alternating curelectrolytic action. As heretofore attempted to be practiced, so-called electrolytic grinding has encountered various .difliculties or the systems or apparatus have inherent limitations or there arise phenomena detrimental to or destructive of the' grinding wheel, and these handicaps become all the more serious where, as is frequently the case, it-is desirable to use diamond grinding wheels,

which are costly. Another dominant aim of this invention is to avoid or alleviate such handicaps, shortcomings or risks by simple, compact, and relatively inexpensive apparatus, and to achieve materially greater over-all efiieiency, whether or not diamond or other'abrasives are employed, by effecting dependable and automatic controls of the conversion of the alternating current energy to direct current energy in response to changes in harmful direction of the electrical conditions at the locus of electrolytic decomposition of the work-piece.

In stock removal by electrolytic decomposition at the work face, the conductive work-piece is made the anode, and at the work-wheel interface, where there may or may not be physical contact and where there may or may not be accompanying abrasive action, there is adequately supplied a suitable electrolyte, which also serves as a coolant, and it is desirable to use high current density since the rate of electrolytic decomposition at the workpiece face is proportional to current flow. Various conditions can occur or be brought into being at the work- Wheel interface that will cause detrimental actions, such as arcing, which can also cause high or excessive rates of wheel wear which, particularly where diamond abrasives are embodied in the wheel, can prove prohibitively costly. It can be shown that a desirable characteristic of supply of direct current for the electrolytic circuit is one where the voltage across the work-Wheel interface is maintained substantially constant up to the point where the electrolytic current flow approaches a critical value above which deleterious arcing occurs, followed by current-limiting action at a selectable current value less than the critical current, to reduce the voltage across the workwheel interface and prevent the current from reaching or exceeding the critical value. A further object of this invention is to effect conversion of alternating current electrical energy into direct current energy at the workwheel interface with the energy conversion controlled in response to conditions at the work-wheel interface so that the just described characteristic of energy supply at the work-Wheel interface is provided in a simple, compact, efiicient and reliable manner.

In describing my invention I prefer to do so in conuection with an electrolytic grinding apparatus in which the grinding wheel, while conductive, also contains abrasive grains and also because certain protective actions which the system of my invention achieves serve also to excellent advantage where both electrolytic and abrasive action take place conjointly, as is frequently desirable in practice. Any suitable mechanism or arrangement may be employed for mounting and driving the conductive grinding wheel and for mounting or supporting, or even for resting thereon for manual movement (as in so-called off-hand grinding), a work-piece, such as a cemented carbide tool or other piece of work or object to be ground or machined, whereby to obtain relative movements between the grinding wheel and the supported work. Many and various forms of mechanism are Well known for cooperatively relating a grinding wheel and a work-piece for relative movement therebetween and providing for various relative adjustments and/or movements between the grinding wheel spindle and the work together with various manual or automatic controls for such adjustments and movements. For eX- ample, I may utilize a machine such as is shown in U. S. Patent 2,101,781, in which a work-table, underlying an adjustably mounted and rotatively driven grinding wheel spindle, is movable and reciprocable relative to the grinding wheel and is mounted on a cross slide for shifting it transversely, that is, forwardly or rearwardly of the machine, relative to the grinding wheel; in the machine of that patent the work-table can be reciprocated upon the transverse or cross slide by manual means or by fluid pressure mechanism as there described, while the cross slide may be manually or mechanically moved to advance the work-table and the work-piece supported by it in steps or at a rate according to the setting of the infeed mechanism or according to the manual actuation thereof, as by a hand wheel. Or, I may utilize a grinding machine, by way of further illustration, of the type or kind disclosed in Patent 2,381,034, the machine of that patent being particularly adapted to shaping tool bits, particularly bits or' tools of the above-mentioned hard cemented carbides, and in that machine the operator manually shifts the holder or carrier that supports the work-piece or tool, relative to an adjustable table or support and relative to the fiat side face of the grinding Wheel, according to various curvatures of surfaces or flat surfaces, sometimes with the aid of templates or with the aid of various adjustments of various angularities, according to the specific character of surface shaping that the particular tool or tool bit requires. These two patented disclosures are illustrative of two of the many types of grinding machines to which our system and controls are applicable for effecting stock removal by electrolytic decomposition at the face of the work-piece.

Accordingly, in the drawings, I have shown in Figures 1 and 2, a driving mounting for the rotating conductive element together with an illustrative work-piece and work-holder or support, with a work-table for the latter depicted largely diagrammatically, particularly in so far as its adjustability and movement relative to the rotating grinding wheel are concerned, inasmuch as such adjustability and movement, and the mechanism for effecting them, may take any suitable or known form, and many thereof are well known in the art.

Thus, the apparatus may have a base or main frame 10 which, at its rear, supports a column or vertical standard 11 which, as indicated by the arrows thereon, is rotatively adjustable about a vertical axis and is also adjustable in up-and-down direction; the column 10 supports a wheel head 12, in which is journaled a grinding wheel spindle 13 which projects both forwardly and rearwardly of the wheel head, and at its rear end carries a pulley 14 which is driven by a belt 15 from a pulley 16 on the shaft of a motor 17, which is suitably carried by the top of the standard 11.

The front end of the spindle 13 is appropriately constructed to have or is provided with means for mounting a grinding Wheel thereon, as by providing it with a tapered portion 21 (Figures 36) that is received into the tapered bore of a fianged sleeve 22, a nut 23 which is threaded onto the spindle 13 holding the flanged sleeve 22 securely in place. The flanged sleeve 22 is suitably constructed to carry and have secured thereto a grinding wheel which is electrically conductive and which is illustratively and preferably constructed, as is shown in Figures 3 and 4 and as is later to be described.

When the grinding wheel is so mounted at the front end of the spindle 13 it substantially overlies or overhangs a work-table 24, which is reversibly movable and reciprocable, as indicated by the double-headed arrow in Figure 1, being supported in suitable lengthwise extending ways provided in the cross slide diagrammatically indicated at 25, the latter being adjustable or movable, reversibly, as indicated by the double-headed arrow in Figure 2, being suitably carried or supported, for that purpose, on suitable ways provided in the base it).

The work-piece W, which for purposes of better illustrating certain features of my invention, may be considered to be a block of cemented carbide and suitable means are provided for releasably holding or clamping it to facilitate control of its movement relative to the operative face of the grinding wheel, and such means may comprise a heavy work-holding bar 27, which is provided with a suitable hole or recess 2 in which the work W is received and in which it is clamped securely, as by a clamping screw 29. in the electrolytic grinding circuit the work W is to serve as the anode in the electrolytic cell and accordingly suitable provision is made for connecting the work W appropriately intothe guardas indicated (seev also Figures and-6).

ewe-gear electrical circuit, and 'suh: means may comprise-a suitably heavy connector screwfiO-bywhich: a5conductormay them-amped, carriedby and threaded into the :work holdting 1mm, as is rbetterzindicated in Figures 3 and 5. The

..vtiorlc=holding bar 27 maywin turn be carried by afi'vise,

generallyiihdicated-at 31; :the vise ma-yibe of- :any suitable flconstr uctionatand may, for example, comprise awfixed iMlSfi'ijHWC-Q'Zuilfid a:mo.vahle vise jaw 33, between which =,ther:;bar 27 may the releasahly' clamped and. held; as by filthfi screw .34, manually operable, has by the handle. 35.

The'visefil .can rest-on the work-table 24, with which, Whentsuitably secured thereto, it is? movable according as the Workstable :24: is moved: oractuated as in the :abovevmentioned Patent 2,161,787,;or relative to; which the vise inlay, hermanually moved, asein the above-mentioned Patent 2381 034; *ineitherricase to-efiect the desired or controlledtraversingrmowement or movements of the work relative to the; grindingzwvhee'l and to effect the desired -eeding;.and-,the retracting movementr or movements there- As indicated; in the drawings,

desired to manually shift or control the movementsof the; visev and work-piecev W relative to the table; In :Figures- 1 and 2 the grinding wheel is generically indicatedbythereference character CR, andby way of-illustrationbut not by way of limitation it is constructed .to present a conductive ring surface at itsflat annular side taco which; according tothe rotational'setting about its vertical; axis,,of the column 11 which supports the wheel-headllmay be given any desired angularity'rela- 1 tive tothelongitudinalipathvof movement-of theimovable work-table 24, according to=the needs of any particular grinding job, buttfor greater simplicity of description'the wheel, head may be considered as set so thatthe plane of theoperative. annular side face of the wheel extends parallel to the linexalong which the work=table 24ris'movable or reciprocable;

A, suitable 'wheel guard-3.8'is provided, -being secured to the wheel head by suitable brackets 39. andbeing providedrwith a hinged-front cover 40-sothataccess to the. wheelspindle IS-may be gained'for mounting or: demounting the grinding wheehthe wheelguard withits cover. iii-may be shaped substantiallyas shown inFigures 1, 2, 5 and 6, beingcut away as shown to expose atsuitableportion-l-of the frontlface of the wheel where the conductive ringsu-rface is operative and-so that the work W'may-be presented thereto, and toexposeacornplementaryback portion. of the 'wheel for purposes, about to bedescribed;

Suitable ,meansareprovided to supply a suitable electrolyte totthe regio-nofcontact or of juxtapositionbetweenthe grinding wheel CR and the work W; such means emaycomprise abroad-mouthed nozzle N, which is preferably adjustably positionable, as by a suitable length of deformable metal tubing-,4 whichcis-connected to and-supported by a rigid pipe 42 secured ';to-thewheel ingly, deformable tube 41 may be manually; bent and setto give the. nozzle N the desired location, the mouth of the nozzle being appropriately dimensioned. todischarge-the liquid electrolyte at and throughout the en- .t irewidthof the conductive ringsurface of the wheel CR, where .the.'vvork-piece W- is presented to the latter.

In Figure l'lzhave shown a tank 44 containing liquid electrolyte AS; the latter can be a solution of sodium chloride in. Water,gpreterably reasonably concentrated;

for example, when the tank is full of pure'water, a sur plus-of common salt may be added thereto so-asto leave a quantity of undissolved salt which simplyrests on the bottom .o-fthe: tank; Other salts can be used,.b ut for Accord chloride are ar -any avoided: saltt such nan e da rmoniac (ammoniuchloride) canes-used.

" bonatesg such as so'diurn carbonateand potassium carbonatacan: be use'dand in some cases may --be preferren, as they are 'som'ewhat less: corrosive than sodium chloride.

Mounted o'n the'c'over plate 46 of'thetztnl 4'4 i's'an electric'motorfiil which drives a pump asrthe-input end of which is connected by a pipe 49 totheinsidbotthe tank 44, with the openendof" the pipe being preferably near the bottom: of the" tank. The output end of the pump 48 is connected by. suitable'piping 50, and-a suitable length of flexible hose S1 toa valve 52' on theend of the pip'e"42 whichis secured to'the hinged: wheeliguard cover 74 0: iAncarrangement such as" just described may be used to supply the work-wheel inter-face adequately with electrolyterfrom that location 'theelectrolyte copiously runs out of the 'bottom of'the wheel guard and it and anygdrippin gsthereof are eventually collected by a .largerpan-53 whichis built around the top edge ofthe work-table'24, and as shown inFigure 2, a spout 54 xcarriedbyvthe' work table and movable therewith dis charges thepamc'ollected liquid into astationary span -55 that,is.-suitablysupported by the base 10 of the machineand whichextends throughout the full lengthof maximum travelof the spout'54-as the lattermoveszwith the worktable -A return pipe 56 extends from' the pan ,the alternatingwurrent energy to provide direct current energy of the earlier above describedcharacteristic-of substantially constant voltage across the workwheel interface followed by current limiting action-with diminished voltage so that critical current values are not reached or exceeded. In one embodiment of my systemand apparatus the wheel mayhave a single conductive face andillustratively, for that purpose, may be constructed as shown in Figures 3 and 5 about to be described in detail, while in another embodiment Qf'my system and apparatus the wheelmay have several conductive surfaces, such as-three, as is illustratively. shown in Figures 4 and- 6 and ill-ustratively constructed in a manner later describedin greater detail.

Referring now to Figures 3 and 5, the single-conductive-faced wheel isvthere generally. indicated by the reference character 60, andin order also to gain certain advantagesin achieving. electrical insulation or isolation, the

vwheel 60v comprises a strong rigid backingB of any Figure 5, and at that face and preferably coaxially.therewith thewheel 60 carries a conductive abrasive ring. CR which presents, in the illustrative construction, an annular conductive face with which the work-piece W andv the electrolytecan coact. This-ring CR may be secured to the backing B in any suitable manner, but preferably the ring is constructed so that 'it is-emb'edded in the non-conductive material of thebacking .B and preferably itflis assembled to the backing itself when the latter is initially molded-out of 'the uncured resinous material-which is,

during the moldingprocess, made to flow about the faces ofrthe ringexcept its operative face and to become interlocked therewith upon curing-of the resinous :or other plastic, as under-heat-and pressure; for, better interlocking thering CR may beof-a conformation that provides a,

continuous annular dovetail D (Figure 3), which can be integrally formed at the back of the ring.

As above indicated, it is sometimes desirable that the rotating conductive element in electrolytic grinding contain abrasive grains and the wheel 60 may be constructed also in a manner to facilitate embodiment of abrasive grains when and where desired. For the grinding of hard cemented carbides, such as those illustratively mentioned above, suitably bonded diamond grains, as of bort, are usually employed because silicon carbide abrasive grains are hardly as effective on cemented carbides, while alumina grains grind them hardly at all. While, in the illustrative embodiments of my invention I prefer to use diamond abrasive grains, grains of other materials, including silicon carbide and aluminum oxide, may be employed, and as is later made clear, in electrolytic grinding, stock removal may be effected solely by electrolytic decomposition of the metal at the work-face without any material abrasive action by any of the grains in the rotating conductive ring or face. Where grains are employed, in order that the ring CR be conductive, the abrasive grains are metal-bonded, and particularly where diamond grains are employed it is preferred that they be embodied in only a relatively small depth in relation to the over-all thickness of the ring itself and accordingly, as is clear from Figure 3, the ring CR comprises an outer abrasive or grain-containing portion 62 of small thickness or depth, and an inner and usually thicker and heavier portion 63 that need not contain any grains and is of metal throughout, serving as a strong rigid support or backing for the thinner diamond-bearing portion 62. Where a dovetail element D is employed, it forms part of the metal backing portion 63, as shown in Figure 3, and may be integrally formed or molded therewith or turned or machined to the desired shape.

In making the conductive abrasive ring CR any suitable or known methods or techniques may be employed and need not be described in detail here. For that matter, the patented art describes how, with the use of powdered metal, to make up a unitary integral abrasive ring or annulus having an outer diamond-bearing abrasive portion and an inner support portion wholly of metal. I might note, however, that a usual method of manufacture comprises placing in a suitably shaped mold, to the desired depth, powdered metal that is to correspond to the nonabrasive backing portion and, after leveling or smoothing off, placing thereover a suitable depth of a mixture of diamond particles and powdered metal, to correspond with the abrasive portion and, after leveling or smoothing off, subjecting the contents of the mold to substantial pressure and then sintering the pressed piece, usually in a protective atmosphere such as hydrogen. By appropriately shaping the mold parts the backing portion 63 may be conformed to have a projecting dovetail part or ring, such as the dovetails D of Figure 3, or, as above noted, and since the backing portion 63 contains no abrasive grains, the dovetails D need not be formed by molding but can be turned or machined to the desired shape after pressing and sintering are completed.

Any suitable metal bond appropriate for bonding the abrasive grains and for giving the rings suitable electrical conductivity may be used. In the abrasive-containing portion of each ring, such as the portions 62 of Figure 3, the concentration of abrasive grains should, of course, not be so great as to detrimentally affect electrical conductivity. For finely divided diamond as the abrasive grain, a concentration thereof in the abrasive portion on the order of 25% or less by volume is suitable. Of the many and various metals that are usable for metal-bonding the diamond grains, I prefer to employ a mixture of copper and tin powders in the proportion of about 82% copper and 18% tin, making for both excellent electrical conductivity and good bonding of the grains, and this same mixture of copper and tin is employed in making up the non-abrasive backings, such as the portions 63 of Figure 3, and I set out the just mentioned mixture of ductive ring-face suitable surface speed for appropriate abrasive action, and suitable means are provided to electrically connect its conductive ring CR into the electrical circuit so that the conductive ring is the cathode, for electrolytic decomposition at the face of the work-piece W; such means conveniently comprises a slip ring constructed and coaxially mounted for rotation with the grinding wheel spindle 13, and a suitable coacting mounting for supporting a brush that bears against the slip ring.

In Figure 3 I have shown such a slip ring at S and it is preferably carried by the non-conductive backing B of the grinding wheel 60, preferably on the back face of the latter, whereby it is also protected, by centrifugal action, against access thereto of electrolytic which the nozzle N (Figure 5) discharges onto the front face, where the conductive ring CR is operative. Conveniently, the slip ring 5 is mounted at the back face of the insulating back B in juxtaposition to the conductive ring CR (Figure 3), and it may be secured in position and electrically connected to the conductive ring CR in any suitable manner.

For example, it may be mounted in position after the back B has been molded and cured with the ring CR interlocked, at the front face, with the cured molded insulating material, and then secured in position by a suitable number of equi-angularly spaced tension tie-members 65, which extend through suitable holes in the back B and are anchored, as by threading, at their inner ends to the conductive ring CR in which tapped holes are provided in the backing portion 63 thereof; the outer ends of these tie-members, which preferably take the form of long screws preferably made of copper or of a copper-tin alloy, extend into suitable countersunk holes in the slip ring S thus to clamp the latter securely and concentrically in position at the back face of the wheel back B and at the same time forming multiple electrical connections of high-current-carrying capacity between the slip ring and the conductive ring CR The screws may be headed, in which case the heads are countersunk into the slip rings, or the screws may be headless, in which case those portions that extend into the countersunk holes in the slip rings may be radially expanded by pressure or by peening to fill up the tapered holes in the slip ring, the taper being appropriately proportioned to the cold-flow characteristics of the metal of the screw shank to facilitate cold-flow expansion thereof as just mentioned. The faces of the slip rings may then be machined, as by turning in a lathe, or by grinding, to be sure that they fall in a plane at right angles to the axis of the grinding wheel and to be sure that the ends of the screws 65 are flush with the faces of their respective slip rings, thus to insure smooth coaction with the brushes of the circuits in which the parts are to coact.

As is better shown in Figure 3, the wheel head 12 has secured to it, as by cap-screws as shown, a bracket 66 which extends in a radial direction relative to the grinding wheel 60 and which is constructed in any suitable way to insulatingly support a brush 67 which is spring-pressed to the left to bear against the face of the rotating slip ring S Suitable means are provided, such as a connector screw 68, for electrically connecting the spring-pressed brush 67 into the energy-supply-and-control circuit.

In Figure 7 the conductive element CR of the grinding wheel 60 and the work W presented to it are diagrammatically shown, together with the slip ring S and brush 67, the latter and the work W being electrically connected by conductors 69 and 70 respectively into the energysupply-and-control system for coaction therewith in responsively controlling or affecting the conversion of alternating current enrgy derived from the power circuit 71--72 to unidirectional current enrgy of the desired and respective voltage and current characteristics-asdictated by conditions at the interface or electrolytic cell of the Work W and rotating conductive part CR The A. C. power circuit 7172 may be of anyof the types usually found in -fact'ories .or' industrial plants and it may be ings :74, 750i a transformer TR, which comprises a shell type of core 76 provided with'two core windows so as to have two outer legs 78, 79 and a center leg 77. The primary windings 74, 75 are on the outer legs 78, 79 respectively and are connected in series as shown, but in such manner that their respectivemagnetic fluxes are additive in the outer legs 78, 79 but oppose each other in the middle leg- 77, and with the windings 74, 75 ,of equal turns their respective flux effects cancel out in the middle leg 77.

I provide the transformer TR with secondary windings 80, 81 for coactionwith the magnetic flux of the primary windings 74, 75 andhence I prefer to position them on the outer legs 78, 79 respectively, as shown; the secondary windings 80, 81 are connected in series by a conductor 82 and by variable taps 84, 85, which are preferably arranged, in any suitable manner, to the conjointly movable or shiftable so that, for whatever output voltage is selected, the same number of turns will be effective in the two windings.

On the middle leg 77 I provide a winding 83, which is to be energized by unidirectional current and which I preferably arrange in circuit with the work-wheel interface and hence in circuit with the electrolytic cell formed by the work W and the rotating conductive ring CR and the electrolyte there-between. For this purpose the circuit arrangement may be as shown in Figure 7.

Thus the output terminals of the serially connected secondary windings 80, 81 are connected by conductors .86, 87 to the two input terminals .of a full-wave rectifier which may be of any suitable construction or arrangement, such as the rectifier bridge RB, diagrammatically shown in the drawings, Withthe output terminals thereof connected to supply unidirectional current to the workwheel interface and to the winding 83 on the middle leg of the transformer, arranged in series therewith. Accordingly, unidirectional current for effecting electrolytic decomposition of the work W, with the latter anodic, can

flow in a circuit that extends'from one output terminal of rectifier RB, by'con'ductor 70, to the work W, and from the rotating conductive part CR by way of slip ring S brush 67', conductor 69, winding 83 on'the' middle leg of the transformer, and by conductor 88 to the other output terminal of the rectifier RB. The winding 83 on therriididleleg is thus unidirectionally energized by the same current' that is effective at the work-wheel interface, and in the middle leg77 of the transformer TR it produces a l nidirectional magneto motive force or flux which, in. magnitude, varies directly with changes in current values at the work-Wheel interface. The magnetic circuit for the unidirectional flux produced bythe winding 83, in the illustrative apparatus, is divided into two complete circ'uits,in which are respectively included" the outer legs78', 79. Since the alternating fluxes produced by the primary windings 74, 75 are not effective in the middle core leg 77, no A. C. voltages are induced in the CD winding 83.

The core 76 is'preferably made of iron or steel or good or high permeability and preferably of substantial or gene erous proportions in relation to-the primary windings 74, 75 and-their respectively coacting secondary windings 80', 81 sothat, with no D. C. energization of the winding 83 on the middle leg 77, the transformer operates at corefiux values well below the knee of the magnetic saturation curve bf thecore :76 and so that, in response to D. C.

onergization of the D. C.'coi1 83, the operating poin't on the saturation curve is shifted in a direction towardthe knee so that the core can begin to saturate. With the worl'. W and rotating wheel part CR and the electrolyte brought into coacting relationship as above described, the D. C. current that flows fromthe work-face through the electrolyte tothe part CR is effective also to unidirectionally energize the saturation-control winding 83 for the same current passes through it'and so long 'as that current is in value, though it may vary, below the selected maximum safe current flow to the electrolytic cell at the work-wheel interface, the corresponding unidirectional flux produced by D; .C. winding 83, while it may shift the operating point of the transformer on the magnetic saturation curve, does not shift it far enough toward the knee to effect material change in the coupling between the primary and secondary A. C. windings and accordingly electrolytic decomposition at the work-face proceeds under conditions of substantial constancy of voltage across the work-wheel interface. I

For any particular type or kind of electrolytic grinding operation the maximum safeacurrent flow may be easily determined; for example, itmay be empirically determined by actual tests, as by observing for different. relations of the work Wto the conductive abrasive ring CR the currentflow to the.work-wheel interface and the voltage thereacross when detrimental arcing takes place, and for such purposes, as well as for purposes of setting the various manual controls, suitable instruments (not shown) such as voltmeters and ammeters, may be used; Thus it maybe found that for a given type of grinding operation the critical current value at which detrimental arcing is produced is, say, 40 amperes, and in such case one might-select a value of 30 amperes as the current value which is'nct to' be materially exceeded across the work-wheel interface, thus to guard against detrimental arcing and the like. Accordingly, the conjointly movable taps 8.4, 85 of the secondary coils of the transformer and also a; tap-90, to which conductor 69 is connecte'd, on the; D; C. winding 83, are appropriately and correspondingly set, 'with the D. C. current tap set to include enough-turns of the D. C. winding 83 so thatwhen the D: current beginsto exceed the selected 30-arnp'ere value, core saturation commences and the transformer operating point on the magnetic. saturation curve moves. along those portions of the magnetic permeability curve that are of rapidly increasing change in slope.

Accordingly, electrolytic decomposition at the workface W may safely proceed even under widely varying electrical conditions in the electrolytic cell, such as changes in area of actual or apparent contact, changes in pressure of actual contact, and the like so long as the'selected current value is'not materially exceeded, and during such action, as above explained, the voltage effecti v'eacros's the Work-wheel interface is substantially con stant. However, should conditions arise at the work-- wheel interface to permit or call for current flow in excess; of the selected 30-a-mpere value, thus to approach the; critical value of arc over, such as the 40-ampere critical value above mentioned illustratively', the increased current flow in the D. C. transformer winding 83 commences: saturation of the transformer core as above described, and with the resultant shift in the operating point on the magnetic curve of the transformer core as above explained, the coupling between the primary and secondary- A. C. windings is reduced and the output voltage of the secondary winding 80--81 drops off rapidly with small increases in the D. C. current beyond the critical value atwhich .core saturation commences, and in that manner the critical value of D. C. current flow is prevented from being reached for so long as the work-wheel inter-face condition that favors arc-over or the like continues to persist.

Thus the electrical condition existent at the work-wheel interface directly, by the resultant current flow thereacross and through the D. C. winding 83 of the transformer TR, determines or selects whether the apparatus, through the transformer TR, functions at substantially constant voltage across the work-wheel interface with permissible variation in current flow thereto, or functions at substantially constant current or current-limiting supply of D. C. energy to the work-wheel interface with variability in downward direction of voltage across the work-wheel interface. Dependably safe electrolytic grinding is thus achieved by a compact and simple and efficient apparatus andreliable protection of the rotating conductive element CR particularly where it comprises also costly abrasive grains, such as diamond bort, is effected to meet the widely varying conditions of interrelationships between the work W and the rotating conductive element CR including also those variables that accompany the type or'kind of work-piece operated upon and correspondingly selectable apparatus or machine for mounting or holding or supporting the work-piece and controlling its relationship to the grinding wheel.

In the above-described system and apparatus I prefer to employ also an inductive reactance, diagrammatically indicated at 91 in Figure 7, including it in the circuit supplying alternating current energy to the primary windlugs 74, 75 of the saturable transformer TR, in order to facilitate certain of the coactions above described and to achieve better effectiveness of the saturation controls effected by the work-wheel interface electrical conditions. More particularly, when the D. C. Winding 83 has its energization increased under the control of the workwheel interface so as to effect core saturation as above described, resulting in reducing the coupling between the primary and secondary A. C. windings, the transformer primary tends to draw increasing magnetizing current, particularly at full-core saturation, and the inductive reactance 91 serves to choke back or to limit to an appropriate value increases in primary winding magnetizing current. For example, I may give the inductor 91 an inductance such that the primary current at full coresaturation does not exceed a value that is, for example, three to five times the rate of primary current at zero D. C. saturation. For this purpose this series inductor 91 can have a reactance suitable thereto and at the same time small enough so that the above-described substantial constancy of voltage when operating before material D. C. core saturation commences is not detri-mentally or undesirably affected as the D. C. current to the workwheel interface varies, during this range or stage of operation of the system. When, however, the stage of core saturation sets in so that drop in voltage across the work-wheel interface takes place to limit the current across the latter the inductive reactance 91, with more current flowing therethrough, as above noted, can take some part in diminishing the D. C. voltage across the work-wheel interface in that it can cause a drop in the effective input voltage applied to the primary windings 74, 75.

By an arrangement as shown in Figure 9 I may, where desired, effect, during the D. C. saturation stage of operation of the transformer TR, a relatively rapid drop in the D. C. voltage applied to the work-wheel interface, as by modifying the series inductive reactor 91 of Figure 7 to provide it with a secondary winding in which an alternating potential is induced and coupling that secondary winding in circuit with the transformer TR so as to aid in diminishing the A. C. voltage output of the secondary windings S0, 81; this is shown in Figure 9, where the modified inductor indicated by the reference character 9i comprises a series primary winding 92 connected in the circuit of the transformer primary windlugs '74, 75, and provided with a suitable core 93 by which the series winding 92 is inductively coupled to a secondary winding 94, which is connected, as shown,

in series with the serially connected transformer second ary windings 80, 81 but in such manner that the voltage induced in the secondary 94 is in opposition to the A. C. voltage of transformer secondary windings 80, 81, so that the effective A. C. voltage applied to the input terminals of the rectifier bridge RE is the difference between-the voltage of the transformer secondaries 80, 81 and the voltage induced in secondary winding 94 of the inductive reactor 91 The latter is suitably proportioned so that, when the transformer TR is Operating below core saturation, the voltage induced in the secondary 94 is much smaller than the voltage of the transformer secondaries 80, 81, for example on the order of one-half of the latter or less, and since the inductive effect of the series winding 92 in the series input circuit to the transformer primary windings is least during operation below transformer core saturation, the effective D. C. voltage across the work-wheel interface is not materially afiected, but as soon as transformer core saturation commences and continues, resulting as above noted in substantial increase in current flow to the transformer primaries, the voltage induced in the inductor secondary 94 rapidly increases and, being opposed to the A. C. voltage of the transformer secondaries 80, 81, the effective A. C. voltage ,applied to the rectifier bridge RB and the effective D. C. voltage across the work-wheel interface are rapidly reduced, reducing with substantially corresponding rapidity the current flowing across the work-wheel interface. For these coactions the ratio of the voltage of inductor secondary 94 to the voltage of the transformer secondaries 80, 81 may also be varied or adjusted not only by secondary winding taps 84, but also by a tap 96 on the inductor secondary 94. Thus protective action at the locus of the electro-decomposition at the work-face, under the direct control of electrical conditions at the latter, can be made effective with great rapidity. With an arrangement such as this the effective D. C. voltage characteristic at the work-Wheel interface can be made more nearly rectangular. Such co-actions and effects as just described can be of substantial advantage where the interrelationship between the work W and the conductive ring CR is subject to sudden or greatly intensified change, as for example, where the work W is manually manipulated as in off-hand grinding or as in the above-mentioned Patent 2,381,034.

Referring to Figures 4 and 6, the grinding wheel there shown may be constructed like the above described single-ring wheel 60 of Figures 3 and 5 except that it is provided with three coaxial conductive abrasive rings CR CR CR embedded in a cured molded non-conductive backing B so as to present their aligned faces at the front annular face of the backing B the latter carrying three coaxially arranged slip rings S S S at the back face thereof and internally connected respectively, by tension tie-members 65, to the conductive abrasive rings C C C The latter may, in their specific construction, be made as above described in connection with the conductive abrasive ring CR of the wheel 60 of Figures 3 and 5, having an abrasive-graincontaining portion 62 backed up by a heavier inner portion 63, which may be given a dovetail shape for interlocking with the molded material of the backing B, as earlier above described, with the conductive tie-members 55 anchored at their respective ends in the portion 63 and in the slip ring, all as above described.

This illustrative multiple-ring wheel 110, when mounted on the driven spindle 46 as shown in Figures 4 and 6, thus presents coaxial aligned conductive surfaces for coaction with the work-piece W, the nozzle N, which discharges the electrolyte as shown in Figure 6, being of a width of mouth to spread the discharged electrolyte onto and throughout the over-all width of the multiple-conductive grinding surfaces of the rings CR CR OR at the region thereof where the work W is presented to them for stock removal by electrolytic decomposition, .the work-piece W beinganodic and being connected into the electrical circuit of Figure 8 by a circuit conductor secured .by the connector screw 30 (Figure 4).

Electrical connection with .theconductive abrasive rings C C C is effected, as the Wheel 110 rotates, by their respective slip rings 8?, S S with which coact respectively stationary spring-pressed brushes 67 67",, 67 (Figure 4) that are carried :by the brush bracket .66, the latter -,carrying insulated connector screws 63, 68*, 68, by which individual circuit conductors may be connected in circuit with the respective brushes and hence with the respective conductive abrasive rings.

It will be understood that the arrangement of three conductive abrasive rings, in the wheel 110, is illustrative and is not to be interpreted by way of limitation; the number of conductiveelements in the wheel may be varied and they may be [less than three in number or more than three.

InF-igure .8 I have diagrammatically shown the three conductive elements 'CR?, CR CR of the wheel 110 operatively related to the work W; as shown in Figures 4 and 6, the conductive elements are closely spaced to each other. Each forms, with the work Wand itheinterposed electrolyte, an electrolytic cell, and in the system as shown in Figure 8 they are connected, through their respective brushes and slip rings, to be supplied with direct current energy individually but in protective coaction with each other. I again employ the saturable transformer TR and rectifier bridge RB, preferably with the series inductive *reactance 91 as in Figure 7, 101 with the transformer inductor 9-1 as in Figure 10, but the D. C. saturating winding 83 on the middle core leg 77 I divide into as many individual windings as there are conductive rings on the wheel 110 and hence illustrative- 14 the transformer ,TRproVide a total of ampere-turns to produce a unidirectional ,flux in the transformer core .such that, so long as the total current flow does not exceed 90 amperes, it may shift -,the operating point of the transformer on the magnetic satura tion cur-ve as the total current .varies below the safe maximum :value :of 90 amperes, but such shifts of :the operatingpoint are principally along a straight-line portioncf thezcore saturation curve and accordingly the coupling between-the primary and secondary transformer windings. is not materially affected and the output voltage ,of :thesecondary wind-- ings is more or less constant, as is also the ;D. C. voltage effective across all three work-wheel interfaces. Should the three work-wheel interfaces, as by uniform increase of pressure of contact between them and the work W, call for more than a total of '90 amperes,.the ampere turns and unidirectional flux of the D. C. windings are so increased as totcornmence saturation of the transformer core as above described, bringing it ionto' or beyond the knee .of-the curve, and :by the resultant change in coupling between the primary and secondary C.

windings, the output voltage of the secondary windings 1y I provide three windings 83 83 83, one terminal of each of which is connected by conductor 88 to one output terminal of the rectifier bridge RB, while the other terminals thereof are connected respectively by conductors 69 69* 69 to the brushes of the respective slip rings of the three conductive abrasive rings CR CR CR preferably through adjustable taps 90 90', 90, which are preferably arranged in any suitable manner to be shifted or set conjointly. For purposes later explained, I prefer to include, in the circuit of each of the several Work-ring interfaces, suitable means for iii suring appropriate coacting controls should conditions at the individual interfaces differ too greatly from one another, and in an illustrative arrangement I include in each of the conductors 69 69', 69 that lead to the several interfaces 2. current-responsive coil, and these are shown, in Figure 8, respectively at 102, 103, 104.

With multiple conductive elements on the rotating wheel 110 it is possible to materially increase the capacity for electrolytic stock removal in that materially higher total current flow and higher current density may be used with reasonably good protection against destructive arcing. For example, in the arrangements of Figures 8 and 1-0, with three conductive wheel elements CR CR CR juxtaposed to the work W, and again assuming that the critical arcing current value is amperes, I am enabled to provide for the flow of a maximum safe current of 30 amperes across each electrolytically-acting interface, so that electrolytic grinding proceeds at a 90-ampere rate, providing three times the capacity for electrolytic decomposition at the work-face; by further increasing the number of conductive elements in the wheel, still greater capacity can be achieved.

Assuming a grinding job in which conditions at the several work-Wheel interfaces are not subject to wide differences from each other, so that the current across each is substantially the same, the three currents flowing respectively through the D. C. windings 83 83, 83 of 81 drops off rapidly, as does also the D. C. voltage across the parallelwork-ring interfaces. :In that manner detrimental arc-over-and like ibad-effects are prevented.

However, as indicated earlier. above, there are' grind- Eing jobs or operations in which electrical conditions at the several work-ring interfacescan vary considerably relative to one another; for example, the work W might make actual or apparent contact withone conductive wheel element and may be completely out of juxtaposition to another, or factual pressure of contact might "be widely .difierent at the several conductive wheel elements. -In such case, while the totallmaximum safe current 'will not .be exceeded, illustratively :the above -amperes, it is possible that .thetotal current does not divide itself equally amongst the three work-ring interfaces and hence an arc-over or other damaging electrical action can take place .at one or two ofthe interfaces. =And where' 'the work W is traversed :or 'reciprocated relativeto the grind 'ing wheel 11 0, as it is run oifofithe wheel, it is juxtaposed to all three conductive Wheel elements at one' point, the -to two'wheel elements, :then to only one, :and finally run out of operative relation completely. An illustrative arrangement for guarding against damaging unequal division .of the total current between the several-electrolytically-acting interfaces may be like that shown in- Figme 18. The series coils =102,"-1'03=, 104' respond tothe respective currents across the three interfaces, and in accordance with the respective interface cur-rents they carry, each'coil is arranged to maintain ,energization of the D. C. saturation winding :on the transformer TR whenever the current across its associated work-ringinterface is interrupted .or .drops below the selected value, and, should. the current across its associated wheel-ring interface begin to exceed the maximum safe currentvalue, illustratively 30 amperes, to increase theenergization of its associated D. C. saturation winding to bring the applied voltage down so that its associatedwork-riug interface is prevented from carrying a damaging value of current. i

In the illustrative arrangement I provide carbon piles CP 6P CP connected so that they are shunted respectively across the three work-ring interfaces W-CR W-CR WCR by way of a conductor 105, which connects one side of each of thethree carbon piles, through a switch 106, to the rectifier bridge output terminal at which the work W is connected, and by conductors 1 03, 109, 111, which respectively connect the other ends of the carbon piles to the other sides of these work-ring interfaces; suitable means are provided to adjust the standards at which these carbon piles operate, such as series variable resistors .112, 113, 114, which are inserted in the respective conductors or lines 108, 109, 1'11.

iEach carbon pile isarranged' so that variable pressure may be applied thereto to vary its resistance, such as a pivoted bell-crank lever 115, one arm of which is arranged to engage the unanchored end of the carbon pile to apply or :release pressure thereon, and the other arm of which has connected thereto a core 116 which is subjected to the flux of the series coil so as to form a solenoid therewith for coaction with an adjustable spring 117 to control the movement of the lever 115. Accordingly, when the current through the series coil is zero or below a selected minimum interface current, spring 117 swings the lever 115 clockwise to relieve the pressure on the carbon pile and to close a switch 118 to short-circuit the carbon pile; switch 118 may be of any suitable construction or arrangement and is simply diagrammatically shown in the drawings as comprising a switch member insulatingly carried on the short arm of the bell-crank lever 115 and thereby movable into or out of engagement with two contacts connected, as shown, across the carbon pile. Suitable means are also provided wherebyapplication of pressure to the carbon pile to decrease its resistance takes place only after the current in the solenoid coil has reached a selected value, which is preferably just above the maximum safe current amperes, as in the above illustration) for the work-ring interface, and below the critical or arcing current (40 amperes, as in the above illustration); such means may comprise a pivoted lever 120, whose free end overlies the free end of the bellcrank lever 115, being held in that relationship by an adjustable spring 121, which normally holds the lever 120 against a limit stop 122.

With this arrangement, should the current at any work ring interface fall to zero or to some selectable low value, such as 10 amperes, which may be selected by correspondingly adjusting spring 117, the latter moves the bellcrank lever clockwise and preferably out of engagement with the free end of the carbon pile, causing closure of the switch 118 and holding that switch closed. Should the current at any Work-ring interface rise above the selected safe current value of 30 amperes, as by reaching a value of amperes, where the critical or arcing current value is amperes, the solenoid winding becomes powerful enough to overcome the spring 121 acting on lever 120 so that lever 115 commences to apply pressure to the carbon pile to decrease its resistance.

I am thus enabled to prevent such inequalities or differences in the conditions at the several work-ring interfaces as are noted above, from permitting such change in the D. C. ampere turns on the middle leg of the transformer TR to become so unequally or differently divided amongst the three D. C. windings 83 83 83 as will allow the amperage in any one of them to reach the critical or arcing current value, illustratively 40 amperes. For example, should the current through any work-ring interface, such as the interface W-CR be reduced to zero, as by movement of the work W out of effective juxtaposition to that wheel-ring, thus reducing to zero the ampere turns in D. C. winding 83 of the transformer and thereby permitting D. C. windings 83 33 to divide the total safe ampere turns of N, the resultant action of coil 102 is to close switch 118 to maintain the current flow through D. C. winding 83 at 30 amperes through a circuit that extends from one terminal of the rectifier bridge RB, conductor (switch 1% being closed), switch 118 (closed), adjustable resistor 112, conductor 108, conductor 69 tap 90 winding 83*, and thence by conductor 88 to the other terminal of the rectifier bridge RB. The inactive condition at work-ring interface W-CR is thus made, through its allocated D. C. winding 83 to supply 30 N ampere turns to the saturation control flux of the transformer TR, leaving 60 N or less ampere turns to be divided between the still active D. C. windings 83", 83, since in the assumed illustration the work W remains operatively related to the two conductive elements CR CR of the grinding wheel 110.

If, now, as between these latter two work-ring interfaces W-CR Vi -CR conditions were to arise in both of them to call for more than 30 amperes in each, the increase in current and in ampere turns in D. C. windings 83*, 83 would be in a direction to exceed the 60 N ampere turns now allotted to these two windings, the operating point on the saturation curve would be shifted into core saturation and, as will now be clear, current limitation follows so that arcing current values cannot be reached.

Should, however, a condition calling for more than 30 amperes arise in only one of these two work-ring interfaces, such as the interface W-CR, as soon as that condition permits a flow of 35 amperes, solenoid coil 103, which up to that point holds the lever in about the position shown (switch 118 being open), with carbon pile CP standing open or at maximum resistance, can now overcome spring 121 and pressure is applied to the carbon pile CF to shunt current in excess of the 35 amperes away from the work-ring interface W CR while permitting that excess current also to pass through the corresponding D. C. winding 83 of the transformer and by that amount increasing the effective D. C. ampere turns to shift the operating point along the magnetic permeability curve, in a direction toward reduction in current output.

If, as between these two work-ring interfaces W-CR and WCR conditions arise where the work W is effectively juxtaposed to only one of them, namely, ring CR there would now be two interfaces, namely, W-CR and JV-CR through which there is no electrolytic current flow, the zero current in solenoid coil 1% effects closure of switch 118 to short-circuit carbon pile (3P maintaining a current of 30 amperes, adjustable by the resistor 113, through D. C. winding 83*, making it effective at 39 N ampere turns, which are thus added to the 30 N ampere turns of D. C. winding 83 which is maintained energized because switch 118 at carbon pile CP maintains its D. C. energizing circuit closed for 30-arnpere current flow; adjustable resistor 112 being set for that Value of current. That, then, leaves 30 N ampere turns to become effective in the D. C. winding 83, which is in the circuit of the still operating work-ring interface W-CR to protect the latter against damaging current values and accordingly, when the current in that interface starts to exceed the selected limiting value of 30 amperes, the resultant increase in saturating flux caused .by winding 83 shifts the operating point of the transformer TR along the saturation portion of the magnetic curve and current limitation promptly ensues, as will now be clear.

If, now, one of the two inactive work-ring interfaces becomes active, such as W-CR the D. C. current flowing in the circuit-of its corresponding D. C. winding 83, which has resistor 113 in circuit therewith, divides between the resistor 113 and the now active work-ring interface JV-CR the latter being now shunted across the resistor 113, and the current flow through solenoid winding 1G3, even though initially small, overcomes spring 117 and moves the lever 115 to open switch 118, which is thereafter held open with the lever 115 in a position where the carbon pile CP is open or of maximum resistance for so long, as will now be clear, as the current in the winding 1% does not reach the intermediate value 01135 amperes, which is needed to move the limit or stop lever 1261 against its spring 121; until that happens, the ampere turns of D. C. winding 83 are proportional directly to the current flow as dictated by re conditions at the work-ring interface VJ-CR for the open or maximum resistance condition of carbon pile C 9 makes the shunt circuit through resistance 113 inelfective to feed current to this winding 33 The current values mentioned above are, it will be understood, illustrative; the apparatus is readily adjustable to function, as above described, at other standards than the illustrative standard above described, as by adaware;

justing the various transformer taps shown in Figures 7710 and, in the systems of Figures 8 and 10, as by adjusting the adjustable spring; 117, 121 and the resistors 112, 113, 114. Moreover, the several parts and elements dependably coact with, and are controlled by, the variable conditions that can exist at the work-wheel interface or interfaces and, moreover, do so, as determined by the variables in the worlowheel interface or interfaces by way of the advantageous characteristic above described whereby these conditions selectably determine whether electrolytic work-face decomposition takes place under substantially constant voltage with variable current or under current-limiting or current-decreasing conditions accompanied by diminishing voltage. Where several work-ring interfaces are employed, the respective variable conditions thereat are dependably brought into interdependence to make the just stated determination un-v der conditions insuring that the saturable transformer, while capable of delivering a total current greatly in excess of the maximum safe current value at any one interface, is prevented from delivering any detrimental or damaging excess to any one interface.

It will thus be seen that there has been provided in this invention an electrolytic grinding system in which the several objects heretofore noted, together with many thoroughly practical advantages, are successfully achieved, The system will be seen to be thoroughly practical, is capable of dependably meeting the requirements of wide? ly vatying types and kinds of grinding operations, and is, moreover, compact, efficient and readily installed in industrial plants or factories equipped with alternating current circuits or source of power. 1

As many possible embodiments may be made of the mechanical features of the above invention and as the art herein described might be varied in various parts, all without departing from the scope of the i wention it is to be understood that all matter hereinabove set forth, or shown in the accompanying drawings, is to be interpreted as illustrative and not in a limiting sense,

I claim:

1. In electrolytic grinding apparatus, in combination, means for supplying alternating current, rotatable com ductive means having a face which rotatively moves rel-. ative to a work-piece, with means for operatively sup? porting a work-piece in juxtaposition to the rotatively moving face of said conductive means and comprising means for supplying an electrolyte to the interface be: tween the supported work-piece and said rotating conductive means whereby interface current may vary with changing conditions at the interface, means for upplying electrical energy to said interface and for limiting current flow across the latter against high-energy arc-over 1 -v prising a transformer having a core with primary winds ings energized from said alternating current supply means and unidirectionally encrgizable control winding means for affecting the saturation of said core and secondary windings of which the magnetic coupling with the pri-. mary windings is affect d by aid control. Windin -me said transformer and its core having the characteristic of operating, for currents in said control winding means less than a selected limiting value, on the sloping. part of its core saturation curve and of operating, at currents thattend to exceed said selected limiting value. at and beyond the, knee in said core saturation curve, said. sec: ondary windings being connected in Circuit, by means which include rectifier means, withsaid interface, the work-piece being positive and said conductive. means negative, and with said control winding means, for uni: directional energization of said control windingmeans to affect the magneticcoupling between the primary and secondary windings and shift the operating point of said transformer and its core along Said Slopingpart of the saturation curve as interface conditions vary current demand up to substantially said selected limiting value and to shi the Oper i g p in to and bey n the-knee 18 in the saturation curve as interface current demand tends to exceed said limiting value whereby the voltage effective at said interface is bstantially constant throughout interface current changes up to substantially said selected value and is diminished as interface current demand tends to exceed said selected value.

2. In grinding apparatus as claimed in claim 1 in which said energy-supplying means comprises means for more rapidly diminishing interface voltage as interface current demands tend to exceed said selected value, said last-mentioned means comprising an inductor connected in series with said primary windings to provide relatively rapid increasing reactance voltage drop thereacross in response to the more rapidly increasing primary winding magnetizing current that is called for as said control winding means shifts said operating point to and beyond said knee and effects saturation of said transformer core.

3. A grinding apparatus as claimed in claim 2 in which said inductor has a secondary winding that responds inductively substantially to the aforesaid rapidly increasing magnetizing current called for by the transformer primary windings, with means interrelating the said sec? ondary winding and said transformer secondary windings to decrease the voltage output of the latter as the voltage of said secondary winding increases.

4. A grinding apparatus as claimed in claim 1 in which said rotatable conductive means comprises a wheel having a conductive part which provides said face with which said work-piece is operatively related and in which said control winding means comprises a winding on S id transformer core, said control winding being connected in series with said interface and responding directly to changes in unidirectional current flow across said interface, the resultant flux produced by said control winding as interface current demand tends to exceed said selected value shifting said operating point to and beyond the knee on the core saturation curve and effecting substantial saturation of said transformer core as the current across said interface begins to exceed said selected value.

5. A grinding apparatus as claimed in claim 1 in which said rotatable conductive means comprises a wheel having a plurality of conductive parts presenting respective adjacent surfaces to provide said face of said conductive means with which said work-piece is operatively related to thereby provide a corresponding plurality of interfaces between the work-piece and said rotating conductive means and in which said control winding means comprises a corresponding plurality of windings on said transformer core, one for each of said interfaces, said plurality of control windings being connected with said plurality of interfaces in respective series circuits and each responding directly to current changes across the interface in its series circuit and conjointly shifting said operating point on the core saturation curve to or beyond said knee and efiecting substantial saturation of said transformer core as the interface currents begin to exceed said selected. value.

6. A grinding apparatus as claimed in claim 5 in which means are provided, one for each of said plurality of interfaces, for supplementary unidirectional energization of its associated control winding in response to a selectable diminution of current across the interface.

7. A grinding apparatus as claimed in claim 5 in which means are provided, one for each of said plurality of interfaces, for supplementary unidirectional energization of its associated control winding in response to a selectable increment of interface current increase toward and adjacent said selected current value and tending to exceed said value.

8. In apparatus for electrical stock removal from a conductive work-piece, in combination, means for supplying alternating current energy, means for effecting'stock removal from a conductive work-piece by unidirectional current flow from the work-piece face through an electrolyte comprising means for supporting the work-piece, conductive means presenting a plurality of conductive parts to which the face of the conductive work-piece is related for current flow through an electrolyte in the direction from the work-piece to said conductive parts, means for fiowing liquid electrolyte onto the face of the conductive work-piece and onto the conductive parts to present liquid electrolyte between said face and said parts, an inductor, a transformer having a core with primary windings connected in a series circuit with said inductor, said series circuit being energized from said alternating current supplying means and said transformer having unidirectionally energizable control windings, one for each conductive part of said conductive means, for affecting the saturation of said core and secondary windings of which the magnetic coupling with the primary windings is affected by said control windings, means for deriving unidirectional current energy from said secondary windings and connected to the conductive work-piece and to said plurality of conductive parts with the former positive and the latter negative, and means for energizing said control windings with unidirectional current comprising means for energizing them in response to the respective changes in the energy dissipated in the current flow from the work-piece to said respective conductive parts, said inductor providing a relatively rapidly increasing reactance voltage drop thereacross in response to increasing primary winding magnetizing current and thereby coacting to diminish the voltage for limiting current flow from the work-piece to said conductive parts.

9. In apparatus for electrical stock removal from a conductive work-piece in combination, means providing a regulatable supply of electrical energy comprising exciting and output windings with means forming a magnetic circuit inductively interrelating them, conductive means, means for supporting a conductive work-piece with means for thereby interrelating the work-piece and said conductive means for relative movement therebetween to effect stock removal from the Work-piece by current flow through an electrolyte between it and said conductive means, means for fiowing liquid electrolyte onto the conductive means and onto the conductive work-piece to present liquid electrolyte between said conductive means and said work-piece, means connecting the output winding to said conductive means and said work-piece, field winding means coacting with said magnetic circuit to afiect the inductive coupling between the output and exciting windings, means for energizing said field winding means substantially proportionately to interface current between said work-piece and said conductive means to vary the aforesaid coupling, and means responsive to field winding energization corresponding to interface current at or above a selected value for lessening the effective excitation supplied by the exciting winding, whereby to effect current limitation across the interface, said conductive means comprising a plurality of conductive elements and said connecting' means comprising conductors connecting the output of said electrical energy supply means in parallel circuits to said conductive elements and said work-piece, the latter being thereby common to said parallel circuits, said field winding means comprising a plurality of field windings and said energizing means comprising connections connecting said field windings in respective series relations to said interfaces whereby said field windings respond to the respective interface currents, each of said parallel circuits having associated therewith means responsive to current-flow interruption at the interface thereof with means activated thereby for providing the corresponding field Winding means with substantially equivalent substitute energization.

10. An apparatus as claimed in claim 9 in which said last-mentioned means comprises means for substantially shunting the interface at which current-flow interruption takes place and thereby maintain energization of the corresponding field winding.

11. In apparatus for electrical stock removal from a conductive work-piece, in combination, means providing 20 a regulatable supply of electrical energy, a plurality of conductive elements, means for supporting a conductive work-piece with means for thereby interrelating the workpiece and said conductive elements for relative movement therebetween to effect stock removal from the work-piece by current flow through an electrolyte between it and said conductive elements whereby the latter when operatively related to the work-piece provide a corresponding. number of interfaces therebetween, means for flowingv liquid electrolyte onto the conductive work-piece and onto the plurality of conductive elements to present liquid" electrolyte between said conductive work-piece and said' plurality of conductive elements, means connecting the output of said supply means in parallel circuits to said conductive elements and said Work-piece, the latter being common to said parallel circuits, regulating means for said electrical energy supply means adapted to regulate the voltage of its output at a level of substantial constancy and having control means therefore, one for each of said interfaces and each comprising a carbon pile for affecting said regulating means and operating means for the carbon pile responsive to interface current to effect current-limiting action by said regulating means.

12. In apparatus for electrical stock removal from a conductive work-piece, in combination, a work-support for the work-piece, a plurality of conductive parts for coaction in electric stock removal from the work-piece face and providing with the latter a plurality of interfaces which are variable as to number and conductivity thereacross as relative movement takes place between the workpiece and said conductive parts, means for flowing liquid electrolyte onto the work-piece and onto the plurality of conductive parts at said plurality of interfaces to present liquid electrolyte between said work-piece and said plurality of conductive parts at said plurality of interfaces, means for supplying electrical energy having conductors for connecting its output in respective parallel circuits to said conductive parts and to the work-piece and having control means adapted to affect the voltage and current of the energy delivered at the output of said supplying means, a plurality of current-responsive means, one for each of said parallel circuits and responsive to the respective interface currents thereof, means comprising means responsive to total interface current for affecting said control means in direction to maintain the voltage across said interfaces substantially constant throughout changes in total interfaces current, whereby the respective interface currents may vary as relative movement takes place between the work-piece and said conductive parts, and means for affecting said control means in direction to depress the voltage across said interfaces and operating under the control of said current-responsive means respectively associated with said parallel circuits, and means limiting the response of each of said current-responsive means to a magnitude of current in its circuit corresponding to interface current tending to exceed a selected safe stock-removal value.

13. In electrolytic grinding apparatus, in combination, a rotatable wheel having a plurality of conductive parts presenting respective adjacent faces, means for supporting a conductive work-piece with means for inter-relating the work-piece and said wheel for relative movement between the work-piece and the said faces of the rotatable wheel, with means for supplying an electrolyte to the interfaces between the supported work-piece and said wheel faces for electrolytic decomposition at the workpiece face, whereby interface current may vary with changing conditions at said interface, means for supplying electrical energy thereto comprising a transformer having a core and primary windings energized by alternating current and having secondary windings together with unidirectionally energizable control winding means for effecting the saturation of said core, said control winding means comprising a plurality of windings, one for each of said interfaces, said transformer and its core having the characteristic of operating, for currents in said control Windmg means less than a selected limiting value, on the sloping part of its core saturation curve and of operating, at currents that tend to exceed said selected limiting value, at and beyond the knee in said core saturation curve, said secondary windings being connected by rectifier means to a plurality of parallel series circuits in each of which is serially included one of said interfaces and one of said control windings, with the work-piece positive and the respective conductive faces negative, for unidirectional energization of said control windings with each responding directly to current changes across the interface in its series circuit and conjointly shifting the operating point of said transformer and its core along said sloping part of the saturation curve as interface conditions vary total. current demand up to substantially said selected limiting value and to shift the operating point to and beyond the knee in said curve as total interface current demand tends to exceed said limiting value whereby the voltage effective at all of said interfaces is substantially constant throughout interface current changes up to substantially said selected value and is variably depressed to effect current limitation as current demand tends to exceed said selected value.

14. In electrolytic grinding apparatus, in combination, a rotatable wheel having a conductive part presenting an operative face, means for supporting a conductive workpiece With means for inter-relating the work-piece and said wheel for relative movement between the work-piece and said face of the rotatable wheel, with means for supplying an electrolyte to the interface between the supported work-piece and said wheel face for electrolytic decomposition at the work-piece face, whereby interface current may vary with changing conditions at said interface, means for supplying electrical energy thereto comprising a transformer having a core and primary windings energized by alternating current and having secondary windings together with unidirectionally energizable control winding means for affecting the saturation of said core, said control winding means comprising a winding, said transformer and its core having the characteristic of operating, for currents in said control winding less than a selected limiting value, on the sloping part of its core saturation curve and of operating, at currents that tend to exceed said selected limiting value, at and beyond the knee in said core saturation curve, said secondary windings being connected by rectifier means to a circuit in which is serially included said interface and said control winding, with the work-piece positive and the conductive wheel face negative, for unidirectional energization of said control winding which responds directly to current changes across the interface in said series circuit and which shifts the operating point of said transformer and its core along said sloping part of the saturation curve as interface conditions vary current demand up. to substan- 15. An electrolytic grinding apparatus as claimed in claim 13 in which means are provided, one for each of said series circuits, and each responding to zero interface current in its series circuit, for providing the corresponding control winding of said control winding means with unidirectional energizing current of a value substantally equal to the aforesaid selected limiting value divided by the number of said interfaces whereby, as interface conditions substantially open-circuit one or more of said series circuits, the control winding or windings of the remaining one or more of said series circuits in which the interface is not open-circuited respond to current changes in the latter to effect shift as aforesaid of the operating point of said core saturation curve.

16. An electrolytic grinding apparatus as claimed in claim 13 in which means are provided, one for each of said series circuits, and each responding to interface current in its series circuit of a magnitude somewhat in excess of said selected limiting value divided by the number of said interfaces, for increasing the unidirectional energiza tion of the control winding in its series circuit and for shunting away from the corresponding interface the ex cess of current over said magnitude of current.

17. An electrolytic grinding apparatus as claimed in claim 16 in which said means, one for each of said series circuits, comprises a variable resistance in shunt relation to the interface in the series circuit, with electromagnetic means operating in response to interface increase above said magnitude of current for decreasing the resistance of said variable resistance.

18. An electrolytic grinding apparatus as claimed in claim 15 in which said means, one for each of said series circuits, comprises switch means in shunt relation to the corresponding interface, with electroresponsive means operating to close said switch in response substantially to open-circuit condition of the corresponding interface.

References Cited in the file of this patent UNITED STATES PATENTS 2,084,870 Schmidt June 22, 1937 2,092,859 Seaverson Sept. 14, 1937 2,245,192 Gugel June 10, 1941 OTHER REFERENCES Keeleric, Steel, vol. 130, No. 3, Mar. 17, 1952, pp. 84 to 86. 

1. IN ELECTROLYTIC GRINDING APPARATUS, IN COMBINATION, MEANS FOR SUPPLYING ALTERNATING CURRENT, ROTATABLE CONDUCTIV MEANS HAVING A FACE WHIHC ROTATIVELY MOVES RELATIVE TO A WORK-PIECE, WITH MEANS FOR OPERATIVELY SUPPORTING A WORK-PIECE IN JUXTAPOSITION TO THE ROTATIVELY MOVING FACE OF SAID CONDUCTIV EMANS AND COMPRISING MEANS FOR SUPPLYING AN ELECTROLYTE TO THE INTERFACE BETWEEN THE SUPPORTED WORK-PIECE AND SAID ROTATING CONDUCTIVE MEANS WHEREBY INTERFACE CURRENT MAY VARY WITH CHANGING CONDITIONS AT THE INTERFACE, MEANS FOR SUPPLYING ELECTRICAL ENERGY TO SAID INTERFACE AND FOR LIMITING CURRENT FLOW ACROSS THE LATTER AGAINST HIGH-ENERGY ARC-OVER COMPRISING A TRANSFORMER HAVING A CORE WITH PRIMARY WINDINGS ENERGIZED FROM SAID ALTERNATING CURRENT SUPPLY MEANS AND UNIDIRECTIONALLY ENERGIZABLE CONTROL WINDING MEANS FOR EFFECTING THE SATURATION OF SAID CORE AND SECONDARY WINDINGS OF WHICH THE MAGNETIC COUPLING WITH THE PRIMARY WINDINGS IS AFFECTED BY SAID CONTROL WINDING MEANS, SAID TRANSFER AND ITS CORE HAVING THE CHARACTERISTIC OF OPERATING, FOR CURRENTS IN SAID CONTROL WINDING MEANS LESS THAN A SELECTED LIMITING VALUE, ON THE SLOPING PART OF ITS CORE SATURATION CURVE AND OF OPERATING, AT CURRENTS THAT TEND TO EXCEED SAID SELECTED LIMITING VALUE, AT AND 